This dictionary says
blow: 2 a : to create a current of moving air by breathing
[no object]
She blew on her fingers to warm them.
He was blowing on his soup to cool it off.
[+ object]
She blew air into the balloon.
But other dictionary says
blow: 3 AIR FROM YOUR MOUTH [intransitive, transitive always + adverb/preposition] to send air out from your mouth
blow (something) into/onto/out etc
She blew onto her coffee to cool it down.
He blew the smoke right in my face.
So, we say:
She blew on or in his face?